Parts of a Water Pump – Car Engine Pump Cut Through

All 8 parts on the diagram

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Pulley The grooved wheel on the front of the shaft. A belt from the engine's crankshaft turns it.
Shaft The shaft that joins the pulley to the impeller.
Bearing Holds the shaft in the housing and lets it spin. A sealed double-row ball bearing.
Housing The cast iron or aluminum body that holds the bearing. It forms the pump chamber round the impeller.
Seal Stops coolant leaking out along the shaft. A spring-loaded seal round it.
Impeller The wheel with blades that spins in the coolant. It flings the coolant outward, pumping it round the engine.
Inlet Where coolant from the radiator comes in. It is near the middle of the impeller.
Outlet Where the impeller pushes the coolant out into the engine's water jacket.

How this list was compiled: Read 2026-09-27. (1) US Army, TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 9-7 and figure 9-3 (coolant from the radiator, coolant to the engine), https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 : a centrifugal pump on the front of the block, receiving coolant from the radiator's lower tank and forcing it through the water jacket; an impeller with blades; driven by the crankshaft through a V-belt; a housing of cast iron or aluminium; the impeller on a shaft supported in the housing on a sealed double-row ball bearing; a spring-loaded seal against leakage. (2) Wikipedia, Centrifugal pump, https://en.wikipedia.org/wiki/Centrifugal_pump : fluid entering the impeller near its axis (the eye), flung outward by the blades into the casing, from which it exits; shaft, bearings and seals. Internal combustion engine cooling, https://en.wikipedia.org/wiki/Internal_combustion_engine_cooling : the water pump's shaft seal and impeller. Pump, https://en.wikipedia.org/wiki/Pump : pumps driven by a belt from an engine. Licence: own work

The drawing: Drawn for this site on 2026-10-05 by script, from plain geometry: profiles about the shaft's axis for the pulley, hub, bearing, seal and housing, and a six-blade impeller held as a small model, shown from the side in the cut pump and alone from the front. Nothing is traced or copied. The layout follows the description and figure 9-3 of the US Army's TM 9-8000, Principles of Automotive Vehicles (1985); the forms were checked by eye against photographs of car water pumps on Wikimedia Commons. Licence: own work

How it works

These are the parts of a car engine's water pump, which keeps coolant moving round the engine, cut through along its shaft with the pulley at the left and the engine block at the right.

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What turns it

A belt from the crankshaft turns the pulley. The pulley turns the shaft, which spins in a sealed ball bearing in the housing's neck. A spring-loaded seal round the shaft keeps the coolant from leaking out along it.

What it pumps

Coolant from the radiator comes in at the inlet, near the middle of the impeller. The impeller's blades fling it outward, and it leaves through the outlet into the engine's water jacket.

A centrifugal pump still lets some coolant circulate after the engine stops, which helps keep it from boiling over.

Questions and answers

What does a water pump do in a car?

It keeps coolant moving: from the radiator, through the passages in the engine where it picks up heat, and back to the radiator to cool.

What drives a car's water pump?

Usually a belt from the engine's crankshaft, turning the pulley on the front of the pump.

What type of pump is a car water pump?

A centrifugal pump: its impeller spins and flings the coolant outward. It moves a lot of coolant for its size, and is not clogged by small bits of dirt.